Semiconductor nanowires and fins, such as those including germanium, are used in a variety of device applications (e.g., in field effect transistors), and may include a surface passivation layer, which can be produced using several techniques. Previously used surface passivation layers are generally very thin (e.g., monolayer thickness) and may include materials that alter the electrical characteristics of the resulting device, for example, materials that have a lattice mismatch with the underlying semiconductor nanowire or fin, or materials that form a dipole at the interface between the passivation layer and the underlying semiconductor nanowire or fin.